Electroless plating of plastics and fibers

ABSTRACT

NYLON DACRON OR OTHER FIBERS OF RABRIC IS PLATED BY FIRST DEGREASING THE FIBRIC WITH AN ORGANIC SOLVENT SUCH AS METHYL ETHYL KETONE, THE FIBRIC IS THEN IMMERSED IN A NOVEL NON-AQUEOUS SOLUTION WHICH SIMULTANEOUSLY FURTHER DEGREASES, CLEANS AND WETS, ETCHES AND INITIATED SENSITIZATION OF THE SURFACE O THE FABRIC FIBERS, THE FABRIC IS THEN RINSED AFTER WHICH IT IS DEGLAZED BY IMMERSION IN AN OXIDIZING SOLUTION, RINSED, IMMERSED IN AMMONIA SOLUTION, TREATED IN A NOVEL SENSITIZING SOLUTION, ACTIVATED IN A NOVEL ACTIVATING SOLUTION, RINSED AND PLATED IN A NOVEL NICKEL OR COPPER PLATING SOLUTION. THE FABRIC MAY BE FURTHER PLATED BY ELECTROPLATING TECHNIQUES.

United States Patent 3,733,213 ELECTROLESS PLATING OF PLASTICS ANDFIBERS George Jacob, Flourtown, Pa., assignor to Coppertech Inc.,Flourtown, Pa. No Drawing. Filed Dec. 31, 1970, Ser. No. 103,296 Int.Cl. C23c 3/02 US. Cl. 117-47 A 9 Claims ABSTRACT OF THE DISCLOSURENylon, Dacron or other fibers or fabric is plated by first degreasingthe fabric with an organic solvent such as methyl ethyl ketone, thefabric is then immersed in a novel non-aqueous solution whichsimultaneously further degreases, cleans and wets, etches and initiatessensitization of the surface of the fabric fibers, the fabric is thenrinsed after which it is deglazed by immersion in an oxidizing solution,rinsed, immersed in ammonia solution, treated in a novel sensitizingsolution, activated in a novel activating solution, rinsed and plated ina novel nickel or copper plating solution. The fabric may be furtherplated by electroplating techniques.

BACKGROUND OF THE INVENTION The present invention relates to electrolessplating of nylon or Dacron and particularly to electrolessly platingnylon and dacron fabrics with nickel or copper.

Chemical plating solutions for depositing metals by autocatalyticchemical reduction of metal ions in solution and in contact with acatalytic surface of the article to be plated are well known. Suchsolutions, which do not use electricity, are referred to in the art aselectroless plating solutions. Electroless metal deposition is alsodistinguished from displacement metal plating of the type described inMetals Finishing Guide Book, 27th edition, 1959, pages 469 et seq., andmetal mirror procedures. Electroless metal plating has found particularuse in plating non-metallic substrates such as ceramics and plastics.

Typically, electroless metal depositions of a non-metallic substratecomprises the separate steps of degreasing the substrate, wetting thesubstrate by immersion in an aqueous detergent solution, oxidizing ordeglazing the substrate, sensitizing the surface of the substrate in anaqueous stannous salt bath, rinsing thoroughly, activating the surfacein a catalytic noble metal salt solution such as palladium chloride andfinally plating the activated substrate in an electroless plating bath.The substrate may then be electroplated to build a thick coating ifdesired.

While the general technique is well known, the particular steps andcompositions of solution useful in the process vary depending upon boththe chemical and physical nature of the substrate to be coated. One setof solutions or conditions for electroless plating may result in acommercially useful product for one substrate but not for another. Amongthe requirements for commercial utility are: solution stability;reproducibility; good adhesion of the deposit; uniformity of deposit forsubsequent electrolytic metal plating; and the production of high lusterof the plated metal.

Electroless plating of nylon and Dacron fabrics with prior arttechniques have not resulted in commercially useful materials. Therequirement for uniformity of coating and good adhesion free ofchipping, peeling or flaking especially after electroplating over theelectroless metal deposit is particularly stringent for plating offabrics which are generally subject to deformation and stress during useand which possess a much larger surface area as compared with solidblock material.

I have developed a process which is particularly useful for theelectroless plating of fibers and fabrics of nylon,

'ice

Dacron, rayon, silk and fiberglass with nickel or copper which leads tosuperior commercially useful products. The novel process is also lesscostly than similar prior art processes and produces smoother, moreuniform and more adherent and bright coatings on these substrates. Thenovel process is, of course, also useful in the plating of these andchemically similar materials in a form other than fibers or fabrics.

SUMMARY OF THE INVENTION A process for electrolessly nickel or copperplating materials comprises; treating the material in a non-aqueoussolution which simultaneously degreases, cleans, wets, etches, andinitiates sensitization of the substrate material; deglazing thesubstrate material in an acid oxidizing solution; rinsing andneutralizing the surface of the material; sensitizing the surface of thematerial with a sensitizing solution containing a non-ionic detergent, astannous salt and an organic reducing agent all dissolved in anonaqueous solvent; activating the material in an aqueous solution ofpalladium chloride; and electrolessly plating the fabric with nickel orcopper.

The process is particularly useful for the plating of fibers or fabricsof nylon, Dacron, rayon, silk and fiberglass. Nylon is a polyamidegenerally produced from the polymerization of an adipic acid derivative;Dacron is a polyester produced from the polymerization of thecondensation product of ethylene glycol with hexamethyl terephthalate;rayon is a cellulose based fiber generally either cellulose acetate orregenerated nitrocellulose.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel process comprises thesteps of:

While it is essential to utilize the combination of the various novelsolutions referred to above in order to obtain optimum commerciallyuseful coatings on nylon and Dacron fabrics, these novel solutions areindividually useful for improving the plating of materials other thannylon or Dacron. For example, the various novel solutions aid inimproving coatings of such materials as polyethylene, polypropylene,polystyrene, polysulfone, epoxy, phenolics, acrylics, vinyls andpolyimides and are useful as substitutes for prior art solutionsperforming similar functions in electroless plating of these materials.

In practice, rinsing steps are generally preferably employed between allother process steps. Also, if the fabric is excessively oily, greasy orotherwise dirty it may be desirable to degrease the fabric with aconventional degreasing solvent, or methyl ethyl ketone, prior toimmersion in the novel non-aqueous multiple acting solution referred toin step (1) supra. This multiple acting solution comprises an organicsolvent having stannous chloride and a non-ionic detergent, such ascommercially available Triton X-lOO, dissolved therein. The solvent mustnot only be capable of dissolving the stannous chloride and detergentbut should also be a good solvent for organic contaminants and capableof etching the fabric surface. The preferred solvent is dimethylformamide. An

optimum composition for this multiple acting solution comprises:

Dimethylformamide /2-1 /z gallons Stannous chloride 100-450 grams TritonX-100 detergent 1-10 cc.

This solution is also useful for obtaining improved electroless platingof polyesters such as mylar, and plating of polyethylene and polyimides.Use of this solution prior to deglazing or oxidizing the substrate isessential for commercially useful results. While the complete action ofthis solution on the fiber or fabric substrate is not fully understood,it is believed that a tin-organic layer is formed on the surface of thesubstrate which enhances sensitization after the deglazing step.

A preferred oxidizing solution useful in the novel process comprises:

Water 400-800 cc. Sulfuric acid 200-800 cc. Chomic acid 30-100 grams Thenovel sensitizing solution of the novel process is identical to themultiple acting solution referred to above. However, optimum results areachieved when from 1 to 20 weight percent formaldehyde is added to thesolution. The formaldehyde may be added as a solid or it may be added asan aqueous solution or non-aqueous solution. For example -40 volumepresent of a 48% formaldehyde solution may be added. These solutions arealso useful for sensitizing materials other than the named fabricmaterials.

The novel aqueous activating solution comprises palladium chloride inhydrofluoric acid. A preferred composition is:

Water /:-1 /2 gallons Palladium chloride 0.1-l /2 grams/gallonHydrochloric acid: 500-1000 cc. 12 N H L/ gal. Concentrated hydrofluoricacid /gogallon Prior art activating solutions contained no HF and it isthe inclusion of HF which aids in giving rise to the improved, uniformactivation obtained with the novel solution. While the inclusion of HPis preferred it is not essential except where the fabric to be plated isnylon. Without HP in the activator, the adhesion of the electrolessmetal and its uniformity on the substrate is extremely poor.

While commercially available electroless nickel or copper plating can beemployed, it is preferred in order to obtain optimum results to use anovel nickel bath or a novel copper bath as set forth in the examplesgiven below.

Subsequent to electroless plating, the fabric may be further plated byconventional electroplating techniques to build up a thick metal layer.Such fabrics have many uses including bullet proof vests, RF shields,static discharge clothes, decorative clothes, heaters and large areachemical catalysts or electrodes.

EXAMPLE 1 A nylon fabric to be plated is first degreased by immersion inmethyl ethyl ketone (MEK) to eliminate any heavy oil formation on thefabric. It is believed that the MEK treatment may also dehydrate thesubstrate surface. This is desirable. The fabric is then immersed in themultiple acting solution for 3-6 minutes at room temperature. Theparticular solution consists of 200 grams of stannous chloride and 5 cc.of Triton X-100 anionic detergent in 1 gallon of dimethylformamide. Thefabric is then rinsed in water and deglazed by immersion for 2-5 minutesat room temperature in an oxidizing solution consisting of 70 grams ofchromic acid dissolved in 600 cc. of water and 500 cc. sulfuric acid.The fabric is then rinsed by immersion for 3-5 minutes in a 50% aqueoussolution of concentrated reagent ammonium hydroxide to neutralize anyexcess acid. This rinse is fol- ,4 lowed by a water rinse. The fabric isthen sensitized by immersion in the multiple acting solution describedabove. The fabric is then thoroughly rinsed prior to the next step. Thefabric is now ready for activation by immersion for 1-6 minutes at roomtemperature in an activating solution consisting of 1 gram of palladiumchloride dissolved in a mixture of 4 gallon of concentrated hydroflouricacid, /2 gallon concentrated hydrochloric acid and 1 /8 gallons ofWater. The activated fabric is then thoroughly rinsed and is finallyplated with either nickel or copper.

A preferred and novel electroless nickel plating bath comprises bothnickel and gold ions in solution which codeposits gold together withnickel on the substrate. A useful formulation consists of 300 grams NiClper gallon of solution. 200 grams per gallon citric acid; 190 grams pergallon lactic acid; 40 cc. per gallon propanoic acid; 1 gram per gallonnon-ionic detergent; 50 grams per gallon sodium hypophosphite and /2grain of gold per gallon either as AuCl or potassium gold cyanide. Theremainder of the solution is water. The solution is brought to a pH offrom about 7-9 with ammonia. The preferred operating temperature of thisbath is between about F.120 F. Plating of a sufiicient thickness isobtained in from about 15-30 minutes. The combination of the namedorganic acids and gold ions together with the nickel ions of the bathare important in yielding supenor coatings.

A preferred novel copper plating bath comprises a copper solutioncontaining in combination ethylene diamine tetraacetic acid (EDTA),lactic acid and sodium carbonate. This combination provides improvedstability of the plating solution and enhances ductility, adhesion andbrightness of the deposit. The concentration of EDTA and lactic acidshould be 20 to 30 grams per gallon of EDTA and between 20-30 grams pergallon lactic acid. Generally, if only EDTA, lactic acid or sodiumcarbonate is used in the absence of each other the bath is eitherunstable and/or the rate of deposition is sluggish and/or the deposit isof poor quality. The copper plating bath is best prepared by combiningequal volumes of two solutions. The first solution comprises:

15-25 gallons deionized water 3-9 gallons NaOH (50% solution) 7-20pounds tartaric acid 15-16 pounds paraformaldehyde 2-6 oz. cobaltsulfate or cobalt acetate 6-18 pounds copper sulfate The pH is adjustedto 6.6-6.7

The second solution comprises:

10-20 gallons water 10-30 gallons sodium hydroxide 2.5-7 lbs. per gallonsodium carbonate 7-21 pounds tartaric acid 2-6 pounds lactic acid/EDTA2/ 3-3/ 2 ratio 50-150 cc. Triton X- What I claim is:

1. An electroless plating process comprises the steps of: (a) treating asurface of a material to be plated, said material being capable of beingwetted and etched by dimethyl formamide, in a non-aqueous solutioncomprising a non-ionic detergent and stannous chloride both dissolved indimethyl formamide; (b) treating the surface with an acidic oxidizingsolution; (c) neutralizing the surface with a basic solution; (d)sensitizing the surface in a sensitizing solution containing incombination, a non-ionic detergent and a stannous salt dissolved innonaqueous solvent; (e) activating the sensitized surface in an aqueouspalladium chloride activating solution; (f) rinsing the surface toremove excess activating solution;

(g) electrolessly plating the activated surface by immersion in anelectroless plating solution.

2. An electroless plating process useful for plating substrates ofpolyamides, polyesters produced from the polymerization of thecondensation product of ethylene glycol with hexamethyl terephthalate,rayon and silk with nickel or copper comprises the steps of: (a)treating the substrate to be plated in a non-aqueous solution comprisingin combination, a non-ionic detergent and a stannous salt both dissolvedin a non-aqueous solvent, said solution simultaneously cleans, wets,etches and initiates sensitization of said substrate; (b) treating saidsubstrate with an acidic oxidizing solution; (c) treating said substratein a solution to neutralize and rinse said acidic oxidizing solution;(d) sensitizing said substrate in a sensitizing solution comprising thecombination of ingredients present in the non-aqueous solution ofparagraph (a) together with an organic reducing agent; (e) activatingthe sensitized substrate in an aqueous activating solution comprisingpalladium chloride and hydrofluoric acid; (f) rinsing said activatedsubstrate, and ('g) clectrolessly plating said activated substrate byimmersion in an electroless plating solution.

3. The process described in claim 2 wherein said nonaqueous solution ofparagraph (a) comprises a non-ionic detergent and stannous chloridedissolved in dimethylformamide and wherein the organic reducing agent insaid sensitizing solution is formaldehyde.

4. The process described in claim 2 including the step of degreasingsaid substrate with methyl ethyl ketone prior to treatment with saidnon-aqueous solution.

5. An electroless plating process for electroless plating of nickel orcopper on a substrate of a polyamide, a polyester, a cellulosederivative, silk and fiberglass comprises the steps of:

(a) treating the substrate to be plated in a solution consistingessentially of the following proportions of materials, /2 to 1 gallonsdimethylformamide, 100-450 grams stannous chloride and a non-ionicdetergent;

'(b) treating said substrate with an acidic oxidizing solution;

(c) neutralizing and rinsing the oxidizing solution from said substrate;

(d) sensitizing said substrate in a sensitizing solution consistingessentially of materials in the following proportions; /z-1 /2 gallonsdimethylformamide,

-450 grams stannous chloride, a non-ionic detergent and -1 to 2-0 weightpercent formaldehyde;

(e) rinsing said substrate;

*(f) activating said substrate in a palladium chloride activatingsolution;

(g) rinsing said substrate; and

(h) metallizing said substrate with an electroless metal plating bath.

6. The process described in claim 5 wherein said activating solutionconsists essentially of materials in the following proportions;

to 1 /2 "gallons Water 0.ll /z grams/ gallon palladium chloride 500-1000cc. 12 N hydrochloric acid/ gallon /2 gallon concentrated hydrofluoricacid solution.

7. The process described in claim 5 wherein said metal plating bath is acopper plating bath.

8. The process described in claim 5 wherein said metal plating bath is anickel plating bath.

9. The process described in claim 8 wherein the nickel plating bathco-deposits gold.

References Cited UNITED STATES PATENTS 3,425,946 2/1969 Emons et al117-47 AX 3,442,683 5/1969 Lenoble et al. 117-47 A RALPH S. KENDALL,Primary Examiner US. Cl. X.R.

